Magnetron



Feb.12,1952 J.KURSHAN Em. 2,585,794

MAGNETRON Filed Oct.v 25. 1947 u 2 SHEETS-SHEET 2 film r l i :SnnentorsTERDME KURSHAN {6MM-Vanaf. if 3 LLI'J'YD 1:. SMITH Patented Feb. 12,1952 VIKMAGNETRON Jerome Kurshan, Princeton, .N...J., and vLloyd-P.

Smith, Ithaca, N. Y., assignors to Radio CorporationofAmerica, acorporation of.Delaware 'Application .October.25, 1947, SerialNo."782,192

l 17.Claims. .'Ihis invention :relates to magnetrons fand particularlyconcerns vmagnetrons 'especially 'suited ffor frequency-modulation.

fWith the usual form l;of`-rnagnetron,l the `variation tof the potentialdifference between the anode and cathode at modulation.frequencies-toproduce frequency-'modulation of the outputalso Yproduces undesirable4and excessive amplitude modulation. YIn.=ana1ysis :of'lthe operating;characteristics of a magnetromgitzhasbeen found that :forfconstantranodecurrent, :the 'power output delpendsuponthe intensity .fofthe'unidirectional or -directcurrent electricfi'eld ator 'near the anodeand that ithe frequency "of .the .oscillations 'generated depends upon:thezmanner in which fthe .intensity `of the lunidirectional ordirectfcurrent Y"e'lectricrleld varies Iwith the-.distance between Ythevanodeand cathode.

vIn accordance lwith-aprimary*object of :the invention, the directlcurrent-lrleldLintensity Anear the anode ismaintainedcsubstantially'constant While Ythe vdirect currentelectricvfield distribution between theanodes-andacathode isvariedratymodulation frequencies, thus tcLobtain frequencymodulation ofthe/magnetron output zat a `'substantially v,constant power level. vMore-zspecically, the relationfbetween the pow-er output fof .fa lmagnetronand frequency*l of lthe'oscillations :gen-- erate'd" by it'arecon'trolled' by "a pair-'of iieldfelec- 'trodes, preferably `infthefformf-offimperforatecylinders coaxial with .the cathode,`-Whose'fringe rfields;extendinto' the spacebetweenfthe electrodes andwhose'direct current :potential .differs 'from that of the anode by asubstantially xedamount, affording the desired frequency-output-characvteristic.

'lIJhe yLinvention .further I:resides fin .th'e methods -ff Joperation/andi theifeatures A of "construction, fcombnation:fand'iarrangement 'hereinafter ldisy'closed Y f Eorl.a :more 'detailedunderstanding ofthe .tin- #Mentionv tand for :illustration of :an:embodiment lthereof, reierenceiisvfmfade to -sthe'iaccompanyin'gdrawings, inzwhich:

: filig. 1, partly :in isection,lzis .a xfrcnt elevationalAAviewrofl-amagnetromtube Fig. 2 is a plan View in section taken:vonzline 2-2 of'Fg. 1;

Fig. 3 is. aside elevational VViewv in section 'taken Yalong line.3-3 ofFig. l;

.F.ig.4v 4 is-an vexploded View of rtheelectrode-as- .sembly showninFigs. rL-.S and .Eig isaschematic circuit diagram .Voir-.a fre-.quencyfmodulated .oscillator Yutilizing the tube .of theprecedingfiigures.

Referring to the drawings, `an elongated,. indirectly-heated cathodelllis disposed axially of `a cylindrical cathode space dened bytwo groupsof anode segments vI I, I2 disposed in a circular array. As Willhereinafter appear, all of the segments of both groups have-the samedirectcurrent potential, and aref-.all of thesame instantaneousmodulating-frequency potential. Atgany .particular instant, however,-the segments II.are.of one polarity and the intervening segments `I2are of vopposite polarity .sofaras .the high-frequency oscillationsgenerated -by the tube-.are concerned. Y Y

Inthe particular form of'magnetron shown,

which utilizes a Ytuned circut--externally of the tube envelope, theanode segments-I I` extend .from the rear lace of a metal plate AI3 atthe Y.tips of lteeth or radial bars `III `iormed `byopeningsl throughthe 1plate and -`equally angular-ly vspa-ced about the axisv ofthelsegment array. Similarly, the Vanode segments I2 extend from the Yfrontface of a metal plate I6 at theltips of teeth I-'I formed by circularopenings or slots .leorsthe like. The openingslof plate I.3,are so`angu- Vlarlystaggered with respectvto the'openings I8 inplate It thatwhen the-plates are intheirassembled position, the two groups ofsegments I I-I Zinterleave to forma cylindrical segmented -anodesurface. l

The plates I3, I-6 are-positioned vWithin the tube envelope by headersI9, .20 of micaor equivalent insulating material, having elongatedpositioning ,slots through which pass the upper andlower ends of thespaced plates. The plates I3, IB are held in their Vproper spacedposition at utheir lowerends by a framework comprising-bars 2|,

22 respectively Welded to the plates I3, I6 :and .-joined` at theirends.bycross bars 23 of glass, or

equivalent.insulatingr material. At .their upper ends, the'plates I3, Itare held in .proper spaced position'vby alframework comprisingbars21d-"25 respectively attached to the plates and joined together byinsulating cross .bars Z6. The anode assembly is held to the upperheader I9 by'terminal clips 21-28 respectively mechanicallyxandelectrically connected to the anode plates I'3-'I6 above the-header andhaving clamping tips 29-30 which extend through openings I3l of theheader vand-.arebent to engage its undersurface.

The terminals 21-28 are respectively Aconnected to `rleads :32, ,.33which .extend through the .tube envelope for connection to an external.tuned circuit, :suchas .aparallel line, .concentric lineY or .thelikepresonant at the frequencyo'f oscillations .generatedbythe-magnetron tube. Y

`disposed internally of the cathode.

The pairs of metal rods 34, 35, held to the lower header 20 by clampingclips 3B, support the cathode I9 and the leads for the heater which isThese rods also extend through the header 29 to support the lower frameformed by the bar members 2I, 22 and 23. Two pairs of bars 3-9, 40extend from the insulating cross bars 26 of the upper frame with theirlower ends respectively attached, as by welding, to condenser plates 43,44, which are insulated from the -outer faces of the plates I3, I6 bythin sheets 45, 46 of mica or similar insulating material. A pair ofbars 41, 48 are attach-ed as by Welding at their upper ends to thecondenser plates 43, 44 and respectively attached at their lower ends toa pair oi iield electrodes 49 and 50. Each of the field electrodes 49,50 is in the form of an imperforate cylinder of thin sheet metal l heldin position close to the anode segments Il,

I2 and concentric with the cathode I 0 by its ycorresponding support 41or 48. The eld electrodes 49, 59 are positioned closer to the anodesegments II, I2 than to the cathode I0, as illustrated `in Fig. l. Thefield electrodes 49, 59 extend a substantial distance into theanode-cathode space from the opposite ends thereof and terminatesubstantially short of one another to leave a substantial intermediateportion of the cathode area directly exposed to the anode segments.

Suitable means, such as the magnets'designated N and S in Figs. 3 and 5,are used to provide a constant magnetic field parallel to the axis ofthe cathode I -to cause the electrons traveling from the cathode to theanode to follow curved paths in the usual magnetron fashion.

Referring to Fig. 5, the anode leads 32, 33 are connected to the openend of a resonant parallel line formed by bars I, 52 along which asnorting bar 53 is slidable for tuning apurposes. The shorting bar isconnected by conductor 54 to the positive terminal of a suitable source55 of constant high direct current voltage whose negative terminal isconnected by conductor 56 to ythe cathodepIU of Vthe magnetron. Theheater leads 51 are connected to a suitable source S of heating currentnot shown.

In accordance with the present invention, the field electrodes 49, 50provide means for maintaining the direct current eld intensity at theanode substantially constant while the direct current electric fielddistribution between the anode andthe cathode is varied at modulationfreqpencies. For the moment assuming absence of the field electrodes 49,50, the oscillations gerierated by the magnetron may befrequency-modulated by superimposing a modulating signal voltage uponthe anode-cathode direct current voltage provided by the source 55; morespecifically, the secondary 58 of a modulating transformer 59 may beincluded in the conductor 55 between the source 55 and the cathode ID ofthe tube, and the primary 60 of the transformer connected to a suitablesource of modulating signal voltage at audio, video or other frequenciessubstantially lower` than the frequency of oscillation of themagnetron.l The resulting frequencymodulation is, however, accompaniedby excessive variation of the output at the modulation 1 frequencies.

`extend into the unobstructed space between the anode and cathodesurfaces. The application of ythe modulating voltage causes the directcurrent j electric field distribution ybetween the anode and cathode tovary with consequent corresponding variation of the frequency of theoscillations generated by the magnetron but because the direct currentelectric field is maintained substantially constant in the vicinity o fthe anode, the frequency modulation is not, as in prior magnetrons,accompanied by substantial amplitudemodulation.

As the exact held-electrode potential which affords minimumamplitude-modulation cannot be precisely predicted, there is pro-vided,in shunt to the direct current voltage source 55, a voltage divider 6Iwhose adjustable contact 62 is connected by lead 63 to the eldelectrodes 49, 50. It

is thus a simple matter, in any particular system,A

to adjust the positive potential of the field-electrodes until thedesired frequency modulationoutput characteristic is obtained.

Although the magnetron specifically illustrated ls of the type using anexternal tuned circuit, it shall be understood the invention isapplicable to the types of magnetron utilizing resonant cavities openinginto the anode-cathode space, for example, the magnetrons may begenerally of the construction disclosed'in -application Serial No.758,692. It shall further be understood that although the magnetrondisclosed herein is one utilizing eight anode segments, the fieldelectrodes may be disposed within the anode-cathode space of a magnetronhaving a larger or smaller number of anode segments. In all cases, it`is desirable that the field electrodes be held at constanthigh-frequency potential by bypassing them to the outside of the anodeplates I3, I6 or equivalent anode block. Although the field electrodeswere included primarily to minimize undesired amplitude-modulation, theyinherently provide a means of altering the frequency-modulationcharacteristics of a multi-segment magnetron and may be utilized toimprove the frequency-modulation characteristic even at sacrifice ofconstancy of output.

What is claimed is:

1. A magnetron comprising anode structure defining a cylindrical anodesurface of constant diameter, a cathode within said anode structure andextending axially of said anode surface, and a hollow cylindricalimperforate eld electrode positionedcloser to said anode surface than tosaid cathode and encircling a substantialpart of said cathode withinsaid anode surface and insulated from said anode structure and saidcathode, a substantial part of the length of ysaid cathode beingdirectly exposed to said anode structure.

2. A magnetron comprising anode structure defining a cylindrical anodesurfaceVa cathode extending axially of said anode surface,and'cylindrical eld electrodes positioned closer t'o said anode surfacethan to lsaid cathode and encircling opposite end regions of saidcathode within said anode surface and insulated from the anode structureand said cathode; a substantial interte f1 mediate por-tion foffthe-cathode V'area fzbeing fdif'rectly exposedtofsaidfanode'estructure.

3.'f=A-1magnetron comprising fanode structure fdeiiriingfaflc'fliriblrical anod'efsurface, a cathode, eX-tending vaxially ofsaifdf-anoide` surf ace, a field electrode 'interposedbetween :a part ofsaid cath- --ode and vsaid anode surface l'for controlling the 4i'direct:fcurrent'iie'ld at said'anode surface, and fabypass Acondenser.internally connectedbetween "said 'iildfflectrodefandf said anodestructure.

4. A magnetron fcomprising segmented f-anode -"st'I-'vucturedefining acylin'z'irical"anode surface, a 'cathode Y'extendingaxially of saidsurface, la vpair "of cylindrical lfeld electrodes respectivelyencircling oppositei ends 'olfsaid' cathode 4and' insulated therefrom,and"bypass condensers respectively connected iinternallyof the magnetronbetween said field electrodes and the outer surface of.

said cathode in a'direction transverse tothe elecl ,tron paththerebetween.a 'field electrode hav- 'ing a -portion 'thereofvinterposed between .substantial por-tions of said anode andsaid-.cathode, a substantial portion of 'the length of said cathodebeing 1 directly exposed to said anode,

andffabypass condenser connected between-said :eld electrode andsaidfianode.

'7. A magnetron comprising an anode, a cathode spaced from said anode,means adjacent said anode for providing a constant magnetic field withinand transverse to the path of electrons between said cathode and saidanode, and field electrodes having portions thereof positioned closer tosaid anode than to said cathode and interposed between the end portionsof said cathode and substantial portions of said anode, the intermediateportion of said cathode between said end portions being directly exposedto said anode.

8. A magnetron comprising an anode, a cathode spaced from said anode,means adjacent said anode for providing a constant magnetic eld withinand transverse to the path of electrons between said cathode and saidanode, and imperforate field electrodes having kportions thereofpositioned closer to said anode than to said cathode and interposedbetween the end portions of said cathode and substantial portions ofsaid anode, the intermediate portion of said cathode between said endportions being directly exposed to said anode.

9. A magnetron comprising an anode structure dening a cylindricalcathode space of constant diameter, an elongated cathode extendingcoaxially within said space, means adjacent said anode structure forproviding a constant magnetic field within said space parallel to saidcathode, and a hollow cylindrical field electrode having a portionthereof positioned closer to said anode than to said cathode andinterposed coaxially between substantial portions of said cathode andsaid anode structure.

1-10. IA' fmagnetron 2comprising ananode-.struclture.deningfa:cylindrical-cathodespacefof-Econ- .'stant"diameter, an felongated'z-cathode 'extending fcoaxially.within"saidtspace=means a'djacentfsaid anode-:structure for providingarconstantmagrietic field-.within sa-idsp'ace parallelftorsaidacath-V.1111.' Aimagnetron comprising :an-anode lstructure defining acylindrical cathode space, an

elongated methoden-extending :fcoaxially rwithin isaid space,irmeansadjacent said :anode structure for j providing a :constant magnetic eldwithin -said space iparallel :to :said-cathode, and axiallyspaced .ihollow ..cylindrical field Aelectrodes having parts Apositioned closer`to said anode :structure .thantc said 4cathode andnterposedcoaxial-'lybetween ther end .portions orisaid lcathode @and substantial portions:of 1 said anode structure, ,the Nintermediate portion :of :said cathode:between -saidfendportions being directly exposed' toisaidanodexstructura l2. -A magnetron comprising an .-anodei strucfturedening a cylindrical Acathode space, van

elongated cathode extending coaxially within said space, meansLad-,iacentsaid fanode structure `for 'providing va constantmagnetic eldwithin said-.space parallel tosaid-cathOde, and axiallyspaced hollowcylindrical imperforate eldelectrodes having `parts positioned .closerto .said

anode structure than to said-cathode andinter- Vposed coaxiallybetweenthe end portions of said cathode 4and substantial portions of said:anode structure, the intermediate portion of said cath- :ode between.said .end Yportions .being directly exposed kto said anode structure.

13. An electrical system comprising a magnetron having an anode, acathode spaced from said anode, and a field electrode having a portionthereof interposed between substantial portions of said cathode and saidanode, a source of variable direct current voltage connected to saidanode and said cathode, and a source of constant direct current voltageconnected to said field electrode and said anode, whereby the directcurrent electric field at said anode and the power output of saidmagnetron are maintained substantially constant despite variations inthe direct current electric field between said anode and said cathodeproduced by variations of said variable voltage source.

14. An electrical system comprising a magnetron having an anode, acathode spaced from said anode, and a field electrode having a portionthereof interposed between substantial portions of said cathode and saidanode, a source of variable direct current voltage connected to saidanode and said cathode, and a source of constant direct current voltageconnected to said eld electrode and said anode, whereby the directcurrent electric iield at said anode and the power output of saidmagnetron are maintained substantially constant despite variations inthe direct current electric field between said anode and said cathodeproduced by variations of said variable voltage source, and a bypasscondenser connected between said field electrode and said anode.

15. An electrical system comprising a magnetron having an anode, acathode spaced from Y, said anode, and a field electrode having a. p0r--tionthereof interposed between substantial portions Aof .said cathodeand said anode, means providing a constant magnetic field within andtransverse to the path of electrons between said cathodeV and saidanode, a source of constant voltage and a source of alternating voltageconnected in series between said anode and said cathode, and a source ofconstant voltage connected to said field electrode and said anode tomaintain the direct current electric field at said anode and the poweroutput of said magnetron substantially constant despite variations inthe direct currentelectric field between said anode and said cathode.

i' 16. An electrical system comprising a magnetron'havng Ian anode, Vacathode spaced from said anode, and a field electrode having a portionthereof interposed between substantial portions of said cathode and saidanode,'means pro- Widing a constant magnetic eld within and transverseto the path of electrons between said cathode and said anode, a sourceof variable direct current voltage connected to said anode and saidcathode to modulate the frequency of oscillations generated by saidmagnetron, and a source of constant direct current voltage connected tosaid ield electrode and said anode, whereby the direct current electriceld at said anode and the power output of said magnetron are lmaintainedsubstantially constant despite variations in the direct current electriceld between said anode and said cathode produced by variations of saidvariable voltage source.

17. An`electrical system comprising a magnetron having an anode, acathode spaced from said anode, and a eld electrode having a portionthereof interposedbetwen substantial portions of said cathode and saidanode, means providing a constant magnetic eld within and transverse tothe path of electrons between said cathode and said anode, a source ofvariable directl current voltage connected to said anode and saidcathode to modulate the frequency of oscillations generated by saidmagnetron, and a source of constant direct current voltage connected tosaid field electrode and said anode, whereby the direct current electricfield at said anode and the power output of said magnetron aremaintained substantially constant ,despite variations in the directcurrent electric eld be` tween said anode and said cathode produced byvariations of said variable voltage source, and means for adjusting thevoltage of said constant voltage source to obtain a desired fref quencymodulation-output characteristic.

JEROME VKURSHAN. LLOYD P. SMITH.

, REFERENCES" CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 943,969 DeForest Dec. 21, 19091,417,912 Hewitt May 30, 1922 1,976,778 Gossling et a1. Oct. 16, 19341,997,053 Gill Apr. 9, 1935 2,000,938 Fay May 14, 1935 2,009,368Usselman July 23, 1935 2,096,249 Kapteyn Oct. 19, 1937 2,115,521 Fritzet al Apr. 26, 1938 2,147,159 Gutton et al Feb. 14, 1939 2,233,261Hollmann Feb. 25, 1941 2,238,272 Linder Apr. 15, 1941 2,416,298 FiskFeb. 25, 1947 FOREIGN PATENTS Number Country Date Y 211,551 GreatBritain Feb. 18, 1924

